52 巻 (2017) 6 号 p. 456-464
The critical temperature Tc and critical current density Jc determine the limits to practical application of superconductors. The superconducting state emerges at Tc from the formation of the Cooper pairs and macroscopic spatial coherence. The current-carrying capability, measured in Jc, is the ability of defects in superconducting materials to pin the magnetic vortices by suppressing the pair potential locally, and this may drive down the Tc of superconducting materials with short coherence length. It is a very difficult and challenging task to raise Tc and Jc simultaneously by introducing defects in the cuprate and iron-based superconducting materials. Here, we review our contribution to understanding the irradiation defect structures in iron-chalcogenide FeSe0.5Te0.5 (FST) superconducting thin films and their correlation to superconducting properties. Using low-energy proton irradiation, we create cascade defects in FST thin films. Tc is enhanced due to the nanoscale compressive strain and proximity effect, while Jc is nearly doubled under a zero field at 4.2 K through strong vortex-pinning by the cascade defects and surrounding nanoscale strain. This route opens up the possibility of engineering the pinning landscape for all superconductors.